Near Field Communication (NFC) is a wireless technology allowing two devices to communicate over a short distance of approximately 10 cm or less. Various protocols using NFC have been standardized internationally within NFC Forum specifications and defined in ISO/IEC 18092, ECMA-340, and ISO 14443, for example. NFC allows a mobile device to interact with a subscriber's immediate environment. With close-range contactless technology, mobile devices may be used as credit cards, to access public transportation, to access secured locations, and many more applications. Contactless systems are commonly used as access control ID's (e.g. employee badges), as well as payment systems for public transportation etc. More recently, credit cards are beginning to include NFC capability.
Typical NFC systems rely on low-frequency signals with structures such as coils or capacitive plates with large fringing electric or magnetic fields to facilitate signal transfer over a short distance. However, these low frequencies limit data rate. To increase data rate, the frequency of the carrier must be increased, and a large bandwidth around that carrier must be allocated.
Permittivity is a material property that expresses a measure of the energy storage per unit meter of a material due to electric polarization (J/V2)/(m). Relative permittivity is the factor by which the electric field between the charges is decreased or increased relative to vacuum. Permittivity is typically represented by the Greek letter ε. Relative permittivity is also commonly known as dielectric constant.
Permeability is the measure of the ability of a material to support the formation of a magnetic field within itself in response to an applied magnetic field. Magnetic permeability is typically represented by the Greek letter μ.
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in a conductor, but only slightly shift from their average equilibrium positions causing dielectric polarization. Because of dielectric polarization, positive charges are displaced toward the field and negative charges shift in the opposite direction. This creates an internal electric field which reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axis aligns to the field. While the term “insulator” implies low electrical conduction, “dielectric” is typically used to describe materials with a high polarizability, which is expressed by a number called the relative permittivity (εr). The term insulator is generally used to indicate electrical obstruction while the term dielectric is used to indicate the energy storing capacity of the material by means of polarization.
Other features of the present embodiments will be apparent from the accompanying drawings and from the detailed description that follows.